Embodiments described herein relate to a particulate filter for capturing particulates in the exhaust of a gasoline or diesel engine, and more particularly, to a particulate filter including a catalyst comprising a mixture of nickel and copper.
In recent years, government regulations in the United States have restricted particulate emissions, which has necessitated improvements in the removal of particulates from diesel and gasoline engine emissions. Such particulates generally consist of carbonaceous particulates in the form of soot. Currently, the most commonly used method for removing soot from engine exhaust is the use of a particulate filter positioned in the engine exhaust which collects soot while allowing exhaust gases to pass through. The collected particulate matter is then burned off (oxidized) at elevated temperatures to clean and regenerate the filter. Regeneration of the deposited particulates must occur in order to prevent the filter from becoming plugged, which can cause an undesirable rise in back pressure to the engine.
However, most commercial filters currently in use are ineffective at burning the deposited particulates at the temperatures encountered under normal operating conditions. In order to lower the burn-off temperature, catalyst washcoats have been applied to the filters to promote soot burning at lower temperatures, typically in the range of about 300° C. to 400° C. Such washcoats typically comprise precious metals such as platinum, palladium, and rhodium and support materials comprised of, for example, alumina, ceria, or ceria-zirconia. However, such catalyzed soot filters are typically expensive to produce due to the high cost of platinum group metals. Another disadvantage of such catalyzed filters is that the bulk of the washcoat is comprised of the support materials, with the active catalyst metals residing primarily in the internal pores of the support. Thus, the direct contact between the active metals and the deposited particulates is limited. While the amount of washcoat may be increased to enhance contact, this results in the undesirable effect of increased backpressure in the engine.
In addition, in situations where the temperature of the engine exhaust is high enough for regeneration, the engine may operate under conditions where there is insufficient oxygen for completing burn-off of the deposited particulates. While the addition of oxygen storage capacity (OSC) materials such as cerium-based oxides may provide additional oxygen, in some vehicle operations, conventional OSC materials do not generate sufficient amounts of oxygen needed for complete burn-off.
Accordingly, there is a need in the art for a particulate filter including a catalyst thereon which provides improved soot oxidation at low temperatures, which does not require the use of platinum group metals, which provides sufficient oxygen storage capacity for burn-off of particulates, and which does not cause an increase in engine back pressure.